KINDS OF BACTERIA

COCCUS, plural Cocci,  in microbiology, a spherical-shaped bacterium. Many species of bacteria have characteristic arrangements that are useful in identification. Pairs of cocci are called diplococci; rows or chains of such cells are called streptococci; grapelike clusters of cells, staphylococci; packets of eight or more cells, sarcinae; and groups of four cells in a square arrangement, tetrads. These characteristic groupings occur as a result of variations in the reproduction process in bacteria. 

BACILLUS (genus Bacillus), any of a group of rod-shaped, gram-positive, aerobic or (under some conditions) anaerobic bacteria widely found in soil and water. The term bacillus has been applied in a general sense to all cylindrical or rod-like bacteria. 

SPIRILLUM,  genus of spiral-shaped bacteria of the family Spirillaceae, aquatic except for one species (S. minus) that causes a type of rat-bite fever in man. The term spirillum is used generally for any of the corkscrew-like species.

Spirillum is microbiologically characterized as a gram-negative, motile helical cell with tufts of whiplike flagella at each end.

VIBRIO,  (genus Vibrio), any of a group of comma-shaped bacteria in the family Vibrionaceae. Vibrios are aquatic microorganisms, some species of which cause serious diseases in humans and other animals.

Vibrios are microbiologically characterized as gram-negative, highly motile, facultative anaerobes (not requiring oxygen), with one to three whiplike flagella at one end.

SPIROCHETE, also spelled spirochaete,  (order Spirochaetales), any of a group of spiral-shaped bacteria, some of which are serious pathogens for humans, causing such diseases as syphilis,yaws, Lyme disease, and relapsing fever. Spirochetes include the genera Spirochaeta,Treponema, Borrelia, and Leptospira.

Spirochetes are gram-negative, motile, spiral bacteria, from 3 to 500 micrometres long.